1. Technical Field
This disclosure relates to a liquid ejecting device and an image forming apparatus including the same.
2. Description of Related Art
As on-demand-type ink jet (IJ) recording techniques, there have been well-known an ink ejecting method in which a vibration plate is provided on a part of the wall of a liquid chamber filled with ink and the vibrating plate is displaced by a piezoelectric actuator or the like so as to change the volume of the liquid chamber and increase the pressure therein, and an ink ejecting method in which a heater to be heated by its energization is provided in a liquid chamber and the inner pressure of the liquid chamber is increased by means of air bubbles generated by heating of the heater. Recently, the IJ technique has been applied not only to a low-price printer but also to image formation for a wide-format poster, a sign board and the like. In a business application or an industrial application, particularly, for improvement of image formation throughput, that is, speeding-up of an image formation rate, are desired, and a method of feeding ink (re-fill) from a high-capacity ink cartridge installed in its body through a tube into a head tank (also called a sub-tank) on the top of a head has been commonly used. When such an ink refill method using a tube is applied, it is possible to lighten and miniaturize its carriage part and accordingly it is possible to miniaturize an apparatus including its structural system and driving system greatly.
As increase of the number of nozzle heads for further improvement of a printing throughput, increase of the flow rate of ink liquid to be fed due to attainment of a high head-driving frequency, and a high viscosity of ink for its short time drying are attained, a problem of insufficient refilling occurs due to the pressure loss of the fluid resistance of a tube. Because the length of a tube is large, particularly, in an apparatus for recording on a large-sized printing medium, the pressure loss is large accordingly and the problem is serious.
Against such a problem, as an ink feeding system disclosed in Japanese Patent Publication Application No. 2006-088564, it may be useful to pressurize ink at its feeding side and to provide a differential pressure regulating valve at the upstream side of a sub-tank whereby ink is fed when the negative pressure of the inside of the sub-tank is greater than a predetermined pressure. The ink feeding system disclosed therein is configured to circulate ink through a reservoir tank fixed on its body and the sub-tank mounted on a carriage whereby it is possible to discharge air bubbles together with the ink. Then, there is provided a difference between the fluid resistances of the feeding route and return route of an ink circulating route, so that the sub-tank is kept at a pressurization state by an ink circulating pressure. A recording head is connected to the sub-tank through the differential pressure regulating valve, and is configured such that ink is fed from the sub-tank to the recording head when the recording head has a predetermined or less negative pressure. Thereby, the aforementioned insufficient refilling may be solved. However, because ink in the sub-tank is merely circulated through the upstream reservoir tank and air bubbles generating in a recording head are merely discharged by means of suction in the ink feeding system, the important efficiency of air bubble discharge of the recording head is insufficient and there is a problem in the stability of ink ejection from a nozzle. In particular, when the length of the head is increased, the efficiency of air bubble discharge may be deteriorated so that sufficient ejection stability may not be ensured.
Meanwhile, an ink feeding system disclosed in Japanese Patent No. 3,252,392 has a configuration so as to provide a good efficiency of air bubble discharge of a recording head part. In the ink feeding system, an ink cartridge and a sub-tank are connected to one side and the other side of a common liquid chamber of a recording head, respectively, wherein pressurization of the ink cartridge and atmospheric pressure release of the sub-tank are conducted appropriately so as to move ink between them whereby it is possible to discharge air bubbles in the common liquid chamber of the head.
As described above, the ink feeding system disclosed in Japanese Patent Application Publication No. 2006-088564 may solve the problem of ink refilling but the efficiency of air bubble discharge of the head may be insufficient when the length of the head is increased, and its ejection stability may not be ensured. In the ink feeding system disclosed in Japanese Patent No. 3,252,392 may provide a good efficiency of air bubble discharge of the head but it is impossible to solve the problem of ink refilling.
In such a situation, the inventor has found that there is provided a liquid ejecting device that does not cause insufficient refilling even in the case where ink feeding with a large flow rate is required, is allowed to discharge an air bubble(s) of a recording head sufficiently, and provides the recording head with an improved ejection stability, and an image forming apparatus with the same.